The present invention relates generally to material handling apparatus and, in a preferred embodiment thereof, more particularly provides a horizontal wrapping machine having an improved article infeed system which permits the machine to be operated with substantially improved speed, reliability and safety.
Horizontal wrapping machines are well known in the material handling art and are utilized to automatically wrap a wide variety of articles in separate packages formed from a continuous sheet of flexible wrapping material supplied to the machine from a large supply roll. Conventional wrapping machines of the type schematically illustrated, for example, in FIG. 1 of U.S. Pat. No. 4,574,566 to Eaves et al., typically include a film forming box for shaping a continuous film of packaging material into a continuous tube; a film drive for operatively drawing the film through the forming box and past a cutting and sealing station; a product infeed drive for feeding products to be packaged through the forming box into the continuous tube of packaging material so that the products are spaced apart from one another in the tube; and a driven rotary cut/seal head at the cutting and sealing station for cutting and sealing the continuous tube of packaging material, to form individual packages, as each product moves through that station.
In conventional wrapping machines of this type, the wrapping material is fed generally downwardly and forwardly to the forming box which operates to downwardly fold and bring together opposite side edge portions of the material which are thereafter sealed together to form the continuous tube. At the rear end of the forming box the tube has an open inlet end into which the products or articles are inserted by means of an endless, multi-link infeed conveyor divided into a series of product-containing flights by spaced apart product pushers or "dogs" carried by the conveyor.
The tube inlet opening rearwardly and upwardly overlaps the discharge end of the conveyor and has a generally V-shaped open bottom portion defined by the down-folded side edge portions of the wrapping sheet as they are being brought together by the forming box to close the tube. Accordingly, the lead drive dog of the conveyor is driven forwardly a substantial distance into the tube inlet opening before dropping through a support plate slot on its way to the rear end of the conveyor. Just prior to dropping through this slot, the lead dog pushes its driven article onto a transfer plate positioned within the forming box just rearwardly of the point at which the down-folded side edges of the wrapping material are laterally brought together to close the tube at the forward end of the forming box. The converging side edge portions of the closing tube grip the article deposited on the transfer plate and forwardly transport it past the front end of the forming box, at which point the tube closes around the article.
As is well known in the wrapping art, this product infeed system can create a variety of problems in the overall operation of the wrapping machine. For example, the lead drive dog can easily tip its delivered article rearwardly and downwardly into the support plate slot through which the lead drive dog drops at the front end of the feed conveyor, thereby causing the article to fall out of the tube, to be crushed as it passes through the cutting and sealing station, or to jam the machine. Additionally, the driven article, as its front end reaches the support plate slot, can tip forwardly into the support plate slot and cause similar problems. Further, there is often a tendency for articles (particularly small ones) to stall on the transfer plate.
Additionally, the necessary entry of each lead drive dog into the tube inlet area can, depending on the conveyor speed, impart an undesirably high degree of forward momentum to the article being inserted into the tube. This, in turn, requires that the end-to-end length of each package be oversized relative to the length of the product being wrapped. The additional wrapping material required, of course, undesirably increases the per article wrapping cost.
To overcome these problems, attempts have been made to use "fall back" drive dogs on the conveyor system. In this conveyor system modification, each drive dog along the top side of the conveyor belt is held upright until it reaches the discharge end of the conveyor, at which time it is permitted to fall rearwardly (by gravity) onto the belt before dropping through the support plate slot. While in theory this would seem to solve both the excess article momentum problem, and the tendency to rearwardly tip the inserted article, neither problem is completely alleviated. For example, as the machine speed is increased, a point is reached at which the gravity fall back of each lead drive dog is simply not fast enough to avoid excessive forward force being imparted by the dog to the inserted article. If the machine is slowed to overcome this problem, the per article wrapping cost is increased. Additionally, at desirable higher machine speeds each lead dog (if not fully retracted by gravity) can still rearwardly tip the article which it is inserting into the tube inlet. Further, the presence of the support plate slot (through which the lead dog drops) can still permit the lead article to forwardly tip thereinto.
One approach to solving these article insertion and feed problems is to construct the wrapping machine in an "inverted" orientation in which the forming box is inverted, and the wrapping material is fed upwardly and forwardly to the rear end of the forming box. In this inverted machine configuration, the forming box upwardly folds side edge portions of the incoming wrapping material and positions the V-opening of the tube inlet above the closed bottom side of the tube inlet portion. This permits the inserted articles to be fed onto the closed side of the tube being continuously formed--at first glance providing the inverted machine with a considerable advantage over its non-inverted counterpart.
However, a considerable portion of this potential advantage is negated by the necessity of spacing the discharge end of the article feed conveyor rearwardly of the tube inlet to avoid interference between each downwardly moving lead dog and the now closed bottom side of the tube inlet. The rearward spacing of the conveyor belt requires the insertion between the belt and the tube inlet of a separate transfer plate onto which each article is deposited on its way into the tube inlet.
The presence of this interposed separate transfer plate requires an auxiliary feed system to slide each deposited article across the transfer plate into the tube inlet, thereby increasing the overall cost of the wrapping machine and adds another mechanical system which must be adjusted and serviced. Additionally, to prevent interference between the transfer plate and the conveyor drive dogs, the rear end of the transfer plate must be provided with a slot through which each lead dog may downwardly pass. This slot provides essentially the same opportunity for undesirable forward and rearward article tipping as the transfer plate within the tube inlet in the non-inverted wrapping machine. Moreover, the article momentum problem, associated with the inline drive dogs, remains.
From the foregoing it can be readily seen that a need exists in horizontal wrapping machinery for an improved article infeed system which eliminates or minimizes the above-mentioned and other problems, limitations and disadvantages typically associated with conventional infeed systems. It is accordingly an object of the present invention to provide such improved infeed system in a horizontal wrapping machine.